Process of producing an alloy steel for hot-working tools



United States Patent 3,360,365 PROCESS OF PRODUCING AN ALLOY STEEL FOR HOT-WORKING TOOLS Norbert Eichler, Bohlerwerk an der Ybbs, Austria, as-

signor to Gebr. Bohler & C0. 'Aktiengesellschaft, Vienna, Austria No Drawing. Filed Apr. 29, 1965, Ser. No. 452,000 Claims priority, application Austria, May 12, 1964, A 4,128/64 4 Claims. (Cl. 75126) Nonaustenitic hot-working steels are used for making tools, forging dies, pressing dies, punches and the like. Such steels consists of 0.200.60% carbon, 1-7% chro mium, 1-18% tungsten, (ll-2% vanadium, up to 5% molybdenum, up to 5% cobalt, up to 5% nickel, balance iron and the usual elements associated with steel. Such tools from these steels are used at temperatures of 400- 700 C. At these operating temperatures and the resulting temperature rise of the tools, these steels are subjected, in addition to other stresses, to hot embrittlement, which may result in brittle fracture. Investigations have shown that the hot embrittlement in such steels in the temperature range of 400-700 C. can be almost completely suppressed by a small addition of cerium and lanthanum in a total amount of the order of 0.008-0.2%, preferably 0.02-0.08%.

It is known that an addition of cerium and lanthanum improves hot-working and toughness. These suggestions in the literature, however,- do not relate to hot-working steels but only to the improvement in toughness at room temperature. Hot embrittlement is a loss in toughness at elevated temperature. In the conventional hot-Working steels, the loss in toughness occurs at a temperature of 450 C. and reaches a maximum between 600 and 650 C.

Hot-working steels which contain cerium and lanthanum exhibit an increase in toughness at temperatures up to 650 C. The toughness decreases only at higher temperatures and this decrease is much lower than with hotworking steels which do not contain creium and lanthanum.

Two experimental melts were made, for example, which contained 0.40% carbon, 0.40% silicon, 0.30% manganese, 2.5% chromium, 4.4% tungsten, 0.3% vanadium, 0.18% sulfur and 0.004% phosphorus. 0.18% ceriumlanthanum alloy was added to one melt when it was tapped into the ladle so that 0.05% cerium and 0.03% lanthanum were retained in the steel. The specimens Were forged down to 2 0 mm. diameter, process-annealed at 1820 C. for two hours and subsequently furnacecooled. Further specimens were quenched in oil from a hardening temperature of 1080 C. and reheated to 640 C. to obtain a strength of 160 kp./sq. mm. The resulting heat-treated specimens were fractured in a hot tensile test at temperatures of 400, 450, 500, 550, 600, 650 and 750 C.

Surprisingly, the elongation values of the heat-treated cerium-lanthanum alloy steels are up to 350% higher than those of normal hot-working steels. The hot-working steel produced from the normal melt and having the same tensile strength had an elongation of 5% at a temperature of 650. On the other hand, the cerium-lanthanum alloy hot-working steels had elongations of 15-20%. Only a temperature increase to 700 C. resulted in a decrease of the elongation of cerium-lanthanum alloy hot-working steels to 12%.

"ice

The reduction in area of cerium-lanthanum alloy steels at 650 C. was found to be 55% whereas hot-working steels produced from a. normal melt and having the same composition in other respects had only a reduction in area of 510% at 650 C. The high-temperature strength and high-temperature yield points are not changed by the addition of cerium-lanthanum.

Thus, the invention provides a process of manufacturing hot-working steels having a reduced hot embrittlement at temperatures between 400 and 700 C. and containing 0.008-0.2%, preferably 0.02-0.08% cerium-lanthanum. According to the invention, cerium-lanthanum may be added as an alloying element to steels containing 02-06% carbon, l7% chromium, 118% tungsten, 0.l2% vanadium, up to 5% cobalt, up to 5% nickel.

The addition of cerium-lanthanum alloy is preferably effected in known manner during the tapping of the melt from the furnace into the ladle. Cerium-lanthanum alloy may also be added during the pouring from the ladle into the ingot mold. It is essential that the total amount of cerium and lanthanum in the steel is 0.008- 0.2%. A plant test has confirmed the test results shown above.

A press die consisting of 0.31% 0.40% manganese, 2.35% chromium, 4.6% tungsten, 0.60% vanadium, 0.05% cerium and 0.03% lanthanumbalance iron and elements accompanying steel, showed in a practical test an increase in service life up to and different from the usual press dies did not fail by brittle fracture but was suitable for re-use when the usual wear had been eliminated.

What is claimed is:

1. A hot-working steel, consisting essentially of 0.2- 0.6% carbon, 1-7% chromium, 112% tungsten, 0.1- 2% vanadium, traces to 5% molybdenum, traces to 5% cobalt, traces to 5% nickel, cerium and lanthanum in a total amount of 0.008-0.2%, balance iron and inevitable impurities.

2. A hot-working steel as set forth in claim 1, which contains cerium and lanthanum in a total amount of 0.02 to 0.08%.

3. A hot-working steel as set forth in claim 1, which has been produced from a melt to which cerium and lanthanum have been added in an amount suflicient to retain in the steel a total amount of cerium and lanthanum between 0.008 to 0.2%.

4. A hot-working steel as set forth in claim 2, which has been produced from a melt to which cerium and lanthanum have been added in an amount suflicient to retain in the steel a total amount of cerium and lanthanum between 0.02 to 0.08%.

carbon, 0.30% silicon,

References Cited UNITED STATES PATENTS 2,104,836 1/ 1938 Hassenbruch 126 X 2,823,992 2/ 1958 Balkcom 75-'-128 X 2,861,908 11/1958 Mickelson 75l28 X 2,876,095 3/1959 Dickerson 75126 2,970,903 2/1961 Mickelson 75126 X DAVID L. RECK, Primary Examiner.

P. WEINSTEIN, Assistant Examiner. 

1. A HOT-WORKING STEEL, CONSISTING ESSENTIALLY OF 0.20.6% CARBON, 1-7% CHRONMIUM, 1-12% TUNGSTEN, 0.12% VANADIUM, TRACES TO 5% MONYBDENUM, TACES TO 5% COBALT, TRACES TO 5% NICKEL, CERIUM AND LANTHANUM IN A TOTAL AMOUNT OF 0.008-0.2%, BALANCE IRON AND INEVITABLE IMPURITIES. 